FIG. 6 shows the configuration of a background-art boiler furnace circuit. Boiler water introduced from an economizer runs into the following circuit. That is, the boil water passing through a spiral water wall 1 is distributed to upper wall side walls 2, an upper wall front wall 3, an upper screen pipe 4 and an upper nose wall 5. After that, the boiler waters passing through the upper wall side walls 2, the upper wall front wall 3 and the upper screen pipe 4 join one another in a ceiling wall 7 while the boiler water passing through the upper nose wall 5 is supplied to auxiliary side walls 6. In FIG. 6, the reference numeral 11 represents a ceiling wall inlet header, and 12 represents a furnace outlet connecting duct.
A rectangular parallelepiped boiler furnace structure is arranged so that a fluid channel is divided into channels corresponding to the respective furnace component surfaces (the upper wall side walls 2, the upper wall front wall 3, the upper screen pipe 4 and the upper nose wall 5), and those channels are linked with one another. Accordingly, it is inevitable that different circuits join one another in the inlet of the ceiling wall 7.
Chiefly in order to reduce temperature differences generated among the upper walls 2 to 4, the connecting ducts 12 between the upper walls 2 to 4 and the ceiling inlet header 11 are designed to be shuffled among the side walls 2, the front wall 3 and the upper screen pipe 4 as shown in FIG. 6, so as to reduce the temperature difference in the ceiling wall 7 caused by temperature differences of fluid among the respective portions.
The connecting ducts 12 are arranged thus to relax the temperature history of the fluid to the ceiling wall 7. Each connecting duct 12 is not always connected to the ceiling wall inlet header 11 close to the connecting duct 12 with a shortest distance. The connecting ducts 12 have a complicated layout as shown in FIG. 6.
Examples of known techniques of such boiler apparatus include JP-UM-A-5-71607, JP-A-2001-33002, etc.
In the background-art boiler apparatus, the connecting ducts 12 connected to the ceiling wall 7 are shuffled to relax the temperature difference in the ceiling wall 7. In fact, however, the temperature difference of fluid cannot be eliminated drastically.
FIG. 7 is a view showing a result of measurement of actual temperature distributions in the furnace wall outlet, the ceiling wall inlet and the ceiling wall outlet. The fluid temperature is high in a portion of the ceiling wall 7 where the connecting duct 12 connected to the front wall 3 is plugged. On the contrary, the fluid temperature is low in a portion of the ceiling wall 7 where the connecting duct 12 connected to each side wall 2 is plugged. Thus, the temperature difference in the inlet of the ceiling wall 7 is so large that the useful life of the ceiling wall 7 is short. Particularly in a transient phase, for example, when there is a variation in a load, when a furnace cleaner (soot blower) is operated, or when a burner is fired on/off, there is a problem that an expected temperature difference reduction effect cannot be obtained.
Further, there is also a disadvantage that the layout of the connecting ducts 12 is so complicated that a large space is required for the duct arrangement, and the working of installing the connecting ducts 12 is troublesome.
In order to solve the foregoing disadvantages belonging to the background art, an object of the present invention is to provide a boiler apparatus which can relieve the reduction of the useful life of a ceiling wall caused by a temperature difference in the ceiling wall and which can simplify the structure.